Beathan was also present at the Battle of Cardassia Prime on the final day of the war, leading a boarding party from USS Tikopai which captured the Breen vessel Triumphant Dawn. His unit was later deployed to Cardassia Prime immediately following the ceasefire as a peacekeeping garrison to help with maintaining law and order until the local Cardassian authorities could resume such duties. ("Darker Than Obsidian")

On one of his peacekeeping patrols, Beathan Lem and his squad discovered a slavery ring run by rogue members of the Central Command and Obsidian Order. When he saw the abuse which the captives had received, he had the criminals rounded up against a wall and then placed weapons in the hands of the former captives, with predictable results, rationalizing that he did what he felt was necessary for the captives to reclaim their lives and dignity. This incident was never reported, and thus cannot be found on any official record. Additional records pertaining to Beathan's service on Cardassia were later sealed by CaptainBreawyn Lem using her diplomatic authority ("Darker Than Obsidian").